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The first hourly observations of thunderclouds and associated lightning events for Tehran area are presented in this paper. Hourly data of Cloud to Ground (CG) lightning events in Tehran area is provided by The World Wide Lightning Location Network (WWLLN). Several indices such as Convective Available Potential Energy (CAPE) and CAPE times total precipitation are examined. Three out of 30 lightning events between 2009 and 2013 in Tehran area with various degrees of agreement with the introduced proxies are investigated in detail using numerical simulations and observations. The spatial correlation and temporal correlation of the lightning strikes are compared with the indices with the goal of developing lightning prediction index as well as a better interpretation of CAPE spatial map. The storm cell area and associated CG lightning are studied to determine the formation, growth, and dissipation phases of the thunderstorm. A physical picture of the observations is obtained and explained using the numerical simulations in this paper as a method for storm nowcasting. This includes an estimation of storm distribution, strike polarity, and complicated structure formation such as anvil, approximate strike location, density, as well as approximate velocity, and direction of propagation to some degrees. To understand the physical properties of the observed treatment of the studied lightning occurrences, numerical simulations were conducted using the WRF-ELEC model. In this regard, the temporal evolution of the net charge, the electric field, and radar reflectivity during the lightning activity was investigated.

This is the second half of a two-part study. In the first part, we had used the World Wide Lightning Location Network's recorded signal amplitudes to test a model of Very Low Frequency signal trans...

The Vector Electric Field Investigation (VEFI) on the C/NOFS satellite comprises a suite of sensors controlled by one central electronics box. The primary measurement consists of a vector DC and AC electric field detector which extends spherical sensors with embedded pre-amps at the ends of six, 9.5-m booms forming three orthogonal detectors with baselines of 20 m tip-to-tip each. The primary VEFI measurement is the DC electric field at 16 vectors/sec with an accuracy of 0.5 mV/m. The electric field receiver also measures the broad spectra of irregularities associated with equatorial spread-F and related ionospheric processes that create the scintillations responsible for the communication and navigation outages for which the C/NOFS mission is designed to understand and predict. The AC electric field measurements range from ELF to HF frequencies.VEFI includes a flux-gate magnetometer providing DC measurements at 1 vector/sec and AC-coupled measurements at 16 vector/sec, as well as a fast, fixed-bias Langmuir probe that serves as the input signal to trigger the VEFI burst memory collection of high time resolution wave data when plasma density depletions are encountered in the low latitude nighttime ionosphere. A bi-directional optical lightning detector designed by the University of Washington (UW) provides continuous average lightning counts at different irradiance levels as well as high time resolution optical lightning emissions captured in the burst memory. The VEFI central electronics box receives inputs from all of the sensors and includes a configurable burst memory with 1–8 channels at sample rates as high as 32 ks/s per channel. The VEFI instrument is thus one experiment with many sensors. All of the instruments were designed, built, and tested at the NASA/Goddard Space Flight Center with the exception of the lightning detector which was designed at UW. The entire VEFI instrument was delivered on budget in less than 2 years.VEFI included a number of technical advances and innovative features described in this article. These include: (1) Two independent sets of 3-axis, orthogonal electric field double probes; (2) Motor-driven, pre-formed cylinder booms housing signal wires that feed pre-amps within tip-mounted spherical sensors; (3) Extended shadow equalizers (2.5 times the sphere diameter) to mitigate photoelectron shadow mismatch for sun angles along the boom directions, particularly important at sunrise/sunset for a low inclination satellite; (4) DC-coupled electric field channels with “boosted” or pre-emphasized amplitude response at ELF frequencies; (5) Miniature multi-channel spectrum analyzers using hybrid technology; (6) Dual-channel optical lightning detector with on-board comparators and counters for 7 irradiance levels with high-time-resolution data capture; (7) Spherical Langmuir probe with Titanium Nitride-coated sensor element and guard; (8) Selectable data rates including 200 kbps (fast), 20 kbps (nominal), and 2 kbps (low for real-time TDRSS communication); and (9) Highly configurable burst memory with selectable channels, sample rates and number, duration, and precursor length of bursts, chosen based on best triggering algorithm “score”.This paper describes the various sensors that constitute the VEFI experiment suite and discusses their operation during the C/NOFS mission. Examples of data are included to illustrate the performance of the different sensors in space.

Methods for the estimation of typhoon eyewall characteristics (the center location, the radius and the width, and radii of inner and outer boundaries) based on World Wide Lightning Location Network (WWLLN) data are presented and discussed in this work. The center locations, the eyewall radii, and inner boundary radii estimated from WWLLN data for the typhoons of the northwestern Pacific from 2011 to 2015 were compared with the typhoon centers, radii of maximum winds, and the radii of the eyes obtained from Advanced Scatterometer (ASCAT) wind data, the Japan Meteorological Agency (JMA) archives, and the Joint Typhoon Warning Center (JTWC) archives. It is shown that the eyewall characteristics estimates based on the lightning discharge data are most closely related to characteristics of the ASCAT wind speed fields, and the radii of the eyewalls and their inner boundaries are linearly related to the radii of maximum winds and the radii of the eyes, with correlation coefficients reaching approximately 0.9 and 0.8, respectively. It was shown that the distances between locations of the eyewalls and typhoon centers estimated according to the WWLLN and those of the ASCAT, JMA, and JTWC data on average were 19, 16, and 17 km, respectively. The eyewall widths varied from 15 to 69 km, with an average of ~30 km.

Contribution of lightning to geomagnetic field variations in ULF ( f 1 Hz) frequency range is estimated within the framework of a simple model of ULF response to lightning strokes. ULF lightning index is introduced to quantify a contribution of lightning to ULF power at observational site. The computed pulse series are compared with the pulse-like interference recorded at the low latitude observatory (KNY). Lightning stroke is modeled as a vertical dipole with the perfectly conducting model ionosphere. A program of automatic detection of pulse-like interference in recorded signal is developed. The analysis of the time series of hourly ULF lightning index at KNY during several weeks in summer of 2012 has shown that the contribution of thunderstorms to ULF power may be significant, especially at frequencies f > 80 mHz. This effect should be taken into account in any application utilizing estimates of local ULF power including seismo-electromagnetics.

WWLLN (World Wide Lightning Location Network) data on global lightning are used to investigate the increase of total lightning strokes at Arctic latitudes. We focus on the summertime data from June...

The paper is devoted to the description of observations over atmospheric and electric effects from volcanic eruptions on Kamchatka peninsula (Russia) and perspectives of their development. To collect information about atmospheric-electric effects accompanying the eruptions of Kamchatka volcanoes, three sensor networks and a VLF radio direction finding station are used. The World Wide Lightning Location Network (WWLLN) provides information on high-current lightning discharges that occur during the development of an eruptive cloud (EC). Variations in the electric field of the atmosphere (AEF E z ), during the passage of EC, were obtained by a network of electric field mills at the sites for volcanic activity observations. Seismic detector network was used to make precision reference to the eruptions. Based on the data obtained, a description is given of the dynamics of eruptions of the most active volcanoes in Kamchatka and the Northern Kuril Islands (Shiveluch, Bezymianny, Ebeko). The paper presents a simulation of the response of the atmospheric electric field, which showed that the approximation by the field of distributed charges makes it possible to estimate the volume charges of EC. The fact of a multi-stage volcanic thunderstorm is confirmed. The first stage is associated with the formation of an eruptive column, and the second with the emergence, development and transfer of EC. Registration of electrical and electromagnetic processes in eruptive clouds can be one of the components of complex observations of volcanic eruptions in order to assess the ash hazard for air transport.

We report on three classes of terrestrial gamma-ray flashes (TGFs) from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) satellite. The first class drives the detectors into paraly...

The 2016–2017 shallow submarine eruption of Bogoslof volcano in Alaska injected plumes of ash and seawater to maximum heights of ~ 12 km. More than 4550 volcanic lightning strokes were detected by the World Wide Lightning Location Network (WWLLN) and Vaisala’s Global Lightning Dataset (GLD360) over 9 months. Lightning assisted monitoring efforts by confirming ash-producing explosions in near-real time, but only 32 out of the 70 explosive events produced detectable lightning. What led to electrical activity within some of the volcanic plumes, but not others? And why did the lightning intensity wax and wane over the lifetime of individual explosions? We address these questions using multiparametric observations from ground-based lightning sensors, satellite imagery, photographs, acoustic signals, and 1D plume modeling. Detailed time-series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level (approximated by − 20 °C temperatures). For example, on 28 May 2017 (event 40), the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume. Model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms, with liquid water contents > 5 g m−3 and vigorous updrafts > 40 m s−1 in the mixed-phase region where liquid water and ice coexist. Based on these findings, we infer that ‘thunderstorm-style’ collisional ice-charging catalyzed the volcanic lightning. However, charge mechanisms likely operated on a continuum, with silicate collisions dominating electrification in the near-vent region, and ice charging taking over in the upper-level plumes. A key implication of this study is that lightning during the Bogoslof eruption provided a reliable indicator of sustained, ash-rich plumes (and associated hazards) above the atmospheric freezing level.

Both ray theory and full-wave models of Very Low Frequency transmission through the ionospheric D-layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low-inclination Communication/Navigation Outage Forecast System satellite to test this semi-quantitatively, for broadband Very Low Frequency emissions from lightning. Approximate ground-truthing of the incident wavefields in the Earth Ionosphere Waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes < 26 deg. Thus our conclusions, too, must be limited to the near-equatorial region, and are not necessarily predictive of mid-latitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of Very Low Frequency lightning emissions through the D-layer, at a level exceeding model predictions by at least an order-of-magnitude. We show that kilometric-scale D-layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D-layer transmission for transmission from powerful man-made radio beacons.

Using 12 years of high-resolution global lightning stroke data from the World Wide Lightning Location Network (WWLLN), we show that lightning density is enhanced by up to a factor of 2 directly over shipping lanes in the northeastern Indian Ocean and the South China Sea as compared to adjacent areas with similar climatological characteristics. The lightning enhancement is most prominent during the convectively active season, November–April for the Indian Ocean and April–December in the South China Sea, and has been detectable from at least 2005 to the present. We hypothesize that emissions of aerosol particles and precursors by maritime vessel traffic lead to a microphysical enhancement of convection and storm electrification in the region of the shipping lanes. These persistent localized anthropogenic perturbations to otherwise clean regions are a unique opportunity to more thoroughly understand the sensitivity of maritime deep convection and lightning to aerosol particles.

The development of a volcanic plume from the Shiveluch volcano explosion on November 16, 2014, is analyzed using a complex of geophysical methods. The start of the explosion was detected by seismic data. The World Wild Lightning Location Network (WWLLN) allowed the localization of volcanic lightning discharges that occurred during the first stage of the eruption plume. Satellite IR monitoring data made the plume structure obvious. An electrostatic fluxmeter mounted 113 km apart from the volcano recorded the first disturbances of the atmospheric electrical potential gradient (PG) at a distance of 90 km from the eruption cloud front. Two distinct PG anomalies, of 50 and 32 min in length and of more than 100 V/m in amplitude, recorded in 2 h, indicate two separate eruption formations formed by this time. The propagation velocities of two parts of the plume close to the wind speeds at altitudes of temperature inversions (9–10 and 12 km), according to balloon sensing, point out to the plume layering and propagation at two altitudes.

Automated wave-feature detection is required to efficiently analyze large archives of broadband Very-Low-Frequency recordings for discrete-whistler identification and feature extraction. We describe a new method to do this, even in the presence of simultaneous, multiple whistler phase dispersions. Previous techniques of whistler identification were unable to deal with simultaneous, multiple phase dispersions. We demonstrate the new method with data from the VEFI payload on the C/NOFS satellite, from the mission years 2008 - 2014

A general lightning data assimilation technique is developed and tested with observations from the World Wide Lightning Location Network (WWLLN). The technique nudges the water vapor mixing ratio toward saturation within 10 km of a lightning observation and is more general than other approaches that require specific model microphysics or flash rates. This approach is applied to both deterministic and ensemble forecasts of the 29 June 2012 derecho event over the eastern United States and a deterministic forecast of the 17 November 2013 convective event over the Midwest using the Weather Research and Forecasting (WRF) Model run at a convection-permitting resolution. Lightning data are assimilated over the first three hours of the forecasts, and the subsequent impact on forecast quality is evaluated. For both events, the deterministic simulations with lightning-based nudging produce more realistic predicted composite reflectivity fields. For the forecasts of the 29 June 2012 event using ensemble data assimilation, forecast improvements from lightning assimilation were more modest than for the deterministic forecasts, suggesting that lightning assimilation may produce greater improvements in convective forecasts where conventional observations (e.g., aircraft, surface, radiosonde, satellite) are less dense or unavailable.

We evaluate nitrogen oxide (NO(sub x) NO + NO2) production from lightning over the Gulf of Mexico region using data from the Ozone Monitoring Instrument (OMI) aboard NASAs Aura satellite along with detection efficiency-adjusted lightning data from the World Wide Lightning Location Network (WWLLN). A special algorithm was developed to retrieve the lightning NOx [(LNO(sub x)] signal from OMI. The algorithm in its general form takes the total slant column NO2 from OMI and removes the stratospheric contribution and tropospheric background and includes an air mass factor appropriate for the profile of lightning NO(sub x) to convert the slant column LNO2 to a vertical column of LNO(sub x). WWLLN flashes are totaled over a period of 3 h prior to OMI overpass, which is the time an air parcel is expected to remain in a 1 deg. x 1 deg. grid box. The analysis is conducted for grid cells containing flash counts greater than a threshold value of 3000 flashes that yields an expected LNO(sub x) signal greater than the background. Pixels with cloud radiance fraction greater than a criterion value (0.9) indicative of highly reflective clouds are used. Results for the summer seasons during 2007-2011 yield mean LNO(sub x) production of approximately 80 +/- 45 mol per flash over the region for the two analysis methods after accounting for biases and uncertainties in the estimation method. These results are consistent with literature estimates and more robust than many prior estimates due to the large number of storms considered but are sensitive to several substantial sources of uncertainty.

Ground-based lightning detection systems geolocated 877 terrestrial gamma ray flashes (TGFs) from a sample of 2,279 TGFs detected with the Fermi Gamma Ray Burst Monitor (GBM). From these accurate geolocations, 24 TGFs are found within the Next Generation Weather Radar (NEXRAD) operational range in the Gulf of Mexico, the Caribbean, and the Pacific near Guam. NEXRAD-enhanced echo-top (EET) data show that these 24 TGFs are consistently adjacent to high-altitude regions of the storms. The high EET values suggest that there is likely a detection–selection effect, in which the gamma rays from lower-altitude TGFs are attenuated by the atmosphere so that such TGFs fall below the detection threshold of current space-based detectors. The vertical integrated liquid density (VILD) values and the volume scan reflectivities Z show that these 24 TGFs originate from storms of a wide range of convective strengths. Convective available potential energy (CAPE) values from reanalysis also vary widely, providing additional evidence of the range of convection in these TGF-producing storms.

Lightning-generated whistler waves are electromagnetic plasma waves in the very low frequency (VLF) band, which play an important role in the dynamics of radiation belt particles. In this paper, we statistically analyze simultaneous waveform data from the Van Allen Probes (Radiation Belt Storm Probes, RBSP) and global lightning data from the World Wide Lightning Location Network (WWLLN). Data were obtained between July to September 2013 and between March and April 2014. For each day during these periods, we predicted the most probable 10 min for which each of the two RBSP satellites would be magnetically conjugate to lightning producing regions. The prediction method uses integrated WWLLN stroke data for that day obtained during the three previous years. Using these predicted times for magnetic conjugacy to lightning activity regions, we recorded high time resolution, burst mode waveform data. Here we show that whistlers are observed by the satellites in more than 80% of downloaded waveform data. About 22.9% of the whistlers observed by RBSP are one-to-one coincident with source lightning strokes detected by WWLLN. About 40.1% more of whistlers are found to be one-to-one coincident with lightning if source regions are extended out 2000 km from the satellites footpoints. Lightning strokes with far-field radiated VLF energy larger than about 100 J are able to generate a detectable whistler wave in the inner magnetosphere. One-to-one coincidences between whistlers observed by RBSP and lightning strokes detected by WWLLN are clearly shown in the L shell range of L = 1–3. Nose whistlers observed in July 2014 show that it may be possible to extend this coincidence to the region of L≥4.

According to World Wide Lightning Location Network (WWLLN) data, a sequence of lightning discharges was detected which occurred in the area of the explosive eruption of Shiveluch volcano on 16 November 2014 in Kamchatka. Information on the ash cloud motion was confirmed by the measurements of atmospheric electricity, satellite observations and meteorological and seismic data. It was concluded that WWLLN resolution is enough to detect the earlier stage of volcanic explosive eruption when electrification processes develop the most intensively. The lightning method has the undeniable advantage for the fast remote sensing of volcanic electric activity anywhere in the world. There is a good opportunity for the development of WWLLN technology to observe explosive volcanic eruptions.

We present refinements of a method of ionospheric D-region sounding that makes opportunistic use of powerful (109–1011 W) broadband lightning radio emissions in the low-frequency (LF; 30–300 kHz) band. Such emissions are from "Narrow Bipolar Event" (NBE) lightning, and they are characterized by a narrow (10-μs), simple emission waveform. These pulses can be used to perform time-delay reflectometry (or "sounding") of the D-region underside, at an effective LF radiated power exceeding by orders-of-magnitude that from man-made sounders. We use this opportunistic sounder to retrieve instantaneous LF ionospheric-reflection height whenever a suitable lightning radio pulse from a located NBE is recorded. We show how to correct for three sources of "regular" variability, namely solar zenith angle, radio-propagation range, and radio-propagation azimuth. The residual median magnitude of the noise in reflection height, after applying the regression corrections for the three regular variabilities, is on the order of 1 km. This noise level allows us to retrieve the D-region-reflector-height variation with solar X-ray flux density for intensity levels at and above an M-1 flare. The instantaneous time response is limited by the occurrence rate of NBEs, and the noise level in the height determination is typically in the range ±1 km.

Lightning is a symptom and a cause of climate change. A recently established task team is working to make lightning data available and useful for climate science and service applications.

Synoptic and mesoscale cyclonic systems over the ocean and seas are often accompanied by thunderstorm activity, the intensity and spatial distribution of which is modulated by the dynamic structure of these systems. Lightning discharges are sources of electromagnetic radiation in the range of very low frequencies (VLF) and are detected by VLF location finders. Using the World Wide Lightning Location Network (WWLLN), relations between characteristics of fields of detected lightning discharges in the north-western part of the Pacific Ocean and those of fields of meteorological elements of weather formations estimated by data of remote sensing of the Earth by satellites are studied by an example of tropical cyclones. We illustrate a technique permitting one to connect thunderstorm activity parameters (frequency and intensity, as well as spatial distribution of lightning discharges) with the structure of weather systems over oceans and seas and with the intensity and forms of mesoscale formations distinguished in these systems by fields of the near-water wind vortex (the fields are obtained using a scatterometer) and by satellite images in the visible and infrared ranges. The relations between the frequency and density of lightning discharges in the range of influence of a tropical cyclone (TC) and spatial distribution of the near-water wind vortex are demonstrated by an example of individual TCs of 2005–2013.

Recent observations from the World Wide Lightning Location Network (WWLLN) reveal a pronounced lightning maximum over the warm waters of the Gulf Stream that exhibits distinct diurnal and seasonal variability. Lightning is most frequent during summer (June–August). During afternoon and early evening, lightning is enhanced just onshore of the coast of the southeastern United States because of daytime heating of the land surface and the resulting sea-breeze circulations and convection. Near-surface wind observations from the Quick Scatterometer (QuikSCAT) satellite indicate divergence over the Gulf of Mexico and portions of the Gulf Stream at 1800 LT, at which time lightning activity is suppressed there. Lightning frequency exhibits a broad maximum over the Gulf Stream from evening through noon of the following day, and QuikSCAT wind observations at 0600 LT indicate low-level winds blowing away from the continent and converging over the Gulf Stream. Over the northern Gulf of Mexico, lightning is most frequent from around sunrise through late morning. During winter, lightning exhibits a weak diurnal cycle over the Gulf Stream, with most frequent lightning during the evening. Precipitation rates from a 3-hourly gridded dataset that incorporates observations from Tropical Rainfall Measuring Mission (TRMM), as well as other satellites, exhibit a diurnal cycle over the Gulf Stream that lags the lightning diurnal cycle by several hours.

We tried to find with the ULF/ELF electric field sensor onboard Chibis-M microsatellite signatures of the IAR (Ionospheric Alfven Resonator) and Schumann resonance (SR) in the upper ionosphere. Whereas observations of the IAR and SR multi-band emissions with ground magnetometers are ubiquitous, in-situ satellite observations of their signatures are very rare. ULF events detected by the Chibis-M show a possibility of triggered excitation of IAR. In contrast to dominating view, IAR has been found to be effectively excited on the dayside, too. Chibis-M observations also supported the possibility of the SR leakage into the upper ionosphere.

Satellites in the Earth's magnetosphere can be used to record the rich electromagnetic wave activity due to terrestrial lightning, typically up to several tens of kilohertz. With simultaneous recordings of the three components of wave electric field E and of the three components of wave magnetic field B, the entire wavefield, polarization, and wave vector can be specified without any appeal to a priori assumptions about the wave mode and without any reliance on the validity of a dispersion relation. However, some satellites lack such a complete suite of measurements. We develop a method which assumes the theoretical dispersion relation for whistler waves then uses recordings of the three components of wave electric field E but no magnetic components to derive the wave polarization and the wave vector (up to a sign ambiguity on the latter). The method can work only because the dispersion relation, which is assumed, already contains information from the full Maxwell's equations. We illustrate the method with 12 s duration simultaneous recordings, at 32 kilosample/s, of three orthogonal components of wave electric field E from the C/NOFS satellite in low-Earth orbit. Our particular example in this article is shown to contain two broadband whistler features in the range of 4–15 kHz, whose wave vectors differ both according to their polar angles from the geomagnetic field B0 and according to their azimuth around the geomagnetic field B0.

The diurnal variation of the global electric circuit is investigated using the World Wide Lightning Location Network (WWLLN), which has been shown to identify nearly all thunderstorms (using WWLLN data from 2005). To create an estimate of global electric circuit activity, a clustering algorithm is applied to the WWLLN data set to identify global thunderstorms from 2010 to 2013. Annual, seasonal, and regional thunderstorm activity is investigated in this new WWLLN thunderstorm data set in order to estimate the source behavior of the global electric circuit. Through the clustering algorithm, the total number of active thunderstorms are counted every 30 min creating a measure of the global electric circuit source function. The thunderstorm clusters are compared to precipitation radar data from the Tropical Rainfall Measurement Mission satellite and with case studies of thunderstorm evolution. The clustering algorithm reveals an average of 660 ± 70 thunderstorms active at any given time with a peak-to-peak variation of 36%. The highest number of thunderstorms occurs in November (720 ± 90), and the lowest number occurs in January (610 ± 80). Thunderstorm cluster and electrified storm cloud activity are combined with thunderstorm overflight current measurements to estimate the global electric circuit thunderstorm contribution current to be 1090 ± 70 A with a variation of 24%. By utilizing the global coverage and high time resolution of WWLLN, the total active thunderstorm count and current is shown to be less than previous estimates based on compiled climatologies.

Author(s): Romps, DM; Charn, AB; Holzworth, RH; Lawrence, WE; Molinari, J; Vollaro, D | Abstract: The contemporaneous pointwise product of convective available potential energy (CAPE) and precipitation is shown to be a good proxy for lightning. In particular, the CAPEn×nP proxy for lightning faithfully replicates seasonal maps of lightning over the contiguous United States, as well as the shape, amplitude, and timing of the diurnal cycle in lightning. Globally, CAPEn×nP correctly predicts the distribution of flash rate densities over land, but it does not predict the pronounced land-ocean contrast in flash rate density; some factor other than CAPE or P is responsible for that land-ocean contrast.

Lightning over the Maritime Continent exhibits a pronounced diurnal cycle. Daytime and evening lightning occurs near coastlines and over mountain slopes, driven by sea and valley breezes. Nocturnal and morning thunderstorms are touched off where land breezes or mountain breezes converge or by gravity waves propagating away from regions of vigorous afternoon convection. In this study, the modulation of the diurnal cycle of lightning and precipitation by 850-hPa winds, cloudiness, and the Madden–Julian oscillation (MJO) is investigated using observations from the World Wide Lightning Location Network (WWLLN) and the Tropical Rainfall Measuring Mission (TRMM) satellite. The 850-hPa wind speed and area-averaged cloudiness are shown to be negatively correlated with day-to-day lightning frequency over land, and thunderstorm occurrence is suppressed windward of, and enhanced leeward of, mountain ranges. Lightning and environmental conditions are similarly related in the MJO. During break periods, the regular diurnal cycle of lightning is enhanced where ambient low-level winds are easterly but abnormally weak—in the Strait of Malacca, over western and southern Borneo and the adjacent seas, and in the region of nocturnal thunderstorms to the west of Sumatra and Java. When the active, cloudy phase of the MJO, accompanied by low-level westerly winds, passes over the Maritime Continent, the regular diurnal cycle of lightning is enhanced leeward (to the east) of the mountains of Java, Borneo, and the Malay Peninsula. The spatial patterns of lightning and rainfall anomalies are broadly similar, but lightning anomalies tend to be more concentrated near coastlines.

[1] The World Wide Lightning Location Network (WWLLN) is used to measure the normalized lightning electric field at three network stations in order to examine the sferic attenuation between the stroke and the station. The electric field measurements are normalized to the radiated very low frequency (VLF) stroke energy to allow direct comparisons of the many stroke-station paths seen by WWLLN. Comparing past theoretical results and models show that WWLLN observes a stronger dependence of VLF propagation on magnetic azimuth compared to past work. The average attenuation over the water of eastward-propagating sferics is found to be 1.13±0.35 dB/Mm during the day and 0.71±0.68 dB/Mm at night, with westward-propagating sferics having average attenuation rates of 2.98±0.68 dB/Mm and 2.66±0.39 dB/Mm for day and night, respectively.